Acetoacetic acid ester derivatives for the manufacture of α-hydroxycarbonyl compounds

ABSTRACT

The invention is concerned with a novel process for the manufacture of compounds of the formula ##STR1## wherein R 1  signifies C 1-5  -alkyl, especially methyl, ethyl, propyl or isopropyl, and the radicals R 2  each independently represent hydrogen or C 1-5  -alkyl, especially hydrogen or methyl, ethyl, propyl or isopropyl. 
     The process is characterized in that a compound of the formula ##STR2## wherein R stands for C 1-4  -alkoxy, chlorine, bromine or C 1-4  -alkanoyloxy, R 1  and R 2  have the above significance and R 3  represents C 1-4  -alkyl. 
     is hydrolyzed and subjected to an aldol condensation and, where R=C 1-4  -alkoxy, the reaction product is subsequently subjected to an acid treatment. 
     The compounds I are for the most part known flavoring substances.

The invention is concerned with a novel process for the manufacture of α-hydroxycarbonyl compounds, especially those of the formula ##STR3## wherein R¹ signifies C₁₋₅ -alkyl, especially methyl, ethyl, propyl or isopropyl, and the radicals R² each independently represent hydrogen or C₁₋₅ -alkyl, especially hydrogen or methyl, ethyl, propyl or isopropyl.

The process in accordance with the invention is characterized in that a compound of the general formula ##STR4## wherein R stands for C₁₋₄ -alkoxy, chlorine, bromine or C₁₋₄ -alkanoyloxy, e.g. acetoxy, propionyloxy, butyryloxy, R¹ and R² have the above significance and R³ represents C₁₋₄ -alkyl, is hydrolyzed and subjected to an aldol condensation.

In this alkaline hydrolysis the ester bonds which are present in II (R in II=C₁₋₄ -alkanoyloxy and the group --COOR³) are cleaved. The aldol condensation yields the compound I.

Where R=chlorine or bromine, only the group --COOR³ is initially cleaved hydrolytically and, after the aldol condensation has been carried out, the halogen residue R must also be hydrolyzed alkalinically.

As the aldol condensation is preferably carried out alkalinically, where R=C₁₋₄ -alkoxy the compound ##STR5## wherein R° stands for C₁₋₄ -alkyl and R¹ and R² have the above significance, which is initially formed in this manner must, of course, thereupon be subjected to an acidic ether cleavage.

Tautomerism is possible where R¹ ≠R² ≠H. Formula I is accordingly intended to embrace both tautomeric forms and their mixtures.

The convenient parameters for the process in accordance with the invention, i.e. the conversion in accordance with the invention of II into I, are indicated in the following Reaction Scheme and Table I relating thereto.

Moreover, this Scheme and Table I contain the convenient parameters for the process for the preparation of the compounds II.

In this Scheme:

R°═C₁₋₄ -alkyl, e.g. as given above,

Me═alkali metal, e.g. Na, K,

AcO═C₁₋₄ -alkanoyloxy, e.g. as given above,

X═Cl, Br.

The novel compounds II are obtained by alkylating a compound of the formula ##STR6##

wherein R, R² and R³ have the above significance, conveniently by means of halocarbonyl compounds in accordance with the Reaction Scheme.

In a particular embodiment in the case of R² ═C₁₋₅ -alkyl (R² in the α-position to the ester group) a corresponding compound III is not used, but the compound of formula II is alkylated prior to its hydrolysis and the aldol condensation which are conveniently carried out without separating the alkylated product. ##STR7##

Table I provides information concerning convenient methods and reagents as well as convenient and preferred reaction parameters for the individual process steps.

                                      TABLE 1                                      __________________________________________________________________________        Type of                                                                     Step                                                                              reaction                                                                               Reagent         T     Literature                                    __________________________________________________________________________     a 1                                                                               Hydrolysis (1)                                                                         Metal hydroxides, metal carbon-                                                                20-100° C.                                                                    H.O. House, Modern Synthetic                  a 3                                                                               alkaline                                                                               ates, metal bicarbonates                                                                             Reactions, 2nd ed. W. A.                         (ester cleav-                                                                          in aqueous solution   Benjamin Inc. Menl. Park,                        age)                          California, 1972, 511 seq.,                      concomitant                   629 seq.                                         aldol conden-                                                                  sation                                                                      a 11                                                                              Enol-ether                                                                             Strong acids e.g. H.sub.2 SO.sub.4,                                                            Reflux                                                                               H.O. House loc, cit. 504                         cleavage (1)                                                                           HCl, H.sub.3 PO.sub.4                                                                          temper-                                                        aqueous solution;                                                                              ature                                                          HI, HBr/CH.sub.3 COOH                                               a 2                                                                               Hydrolysis (1)                                                                         Alkaline conditions:                                                                           20-100° C.                                              Metal hydroxides, e.g. alkali                                                  metal hydroxides, alkaline                                                     earth metal hydroxides,                                                        preferably in aqueous solution.                                                aqueous ammonia solution                                            a 22                                                                              Hydrolysis (1)                                                                         Weakly basic:   20-100° C.                                                                    H.O. House, loc. cit.,                           alkaline                                                                               Metal carbonates, metal bi-                                                                          511 seq., 629 seq.                               (ester cleav-                                                                          carbonates                                                             age)    in aqueous solution                                                    concomitant                                                                    aldol conden-                                                                  ation                                                                       b 1                                                                               Substitution                                                                           Alkali alcoholate in excess:                                                                   prefer-                                                                              EP-PS 76,378                                     (alkoxylation)                                                                         aprotic solvent, e.g.                                                                          ably  CH-PS 562,191                                            acetonitrile, propionitrile,                                                                   50-100° C.                                              etc.                                                                b 3                                                                               Substitution                                                                           Reaction with a metal alkan-                                                                   50-100° C.                                                                    Kato et al. J. C. S. Perkin I,                   (acyloxyl-                                                                             oate in polar aprotic solvents,                                                                      (1979), 529                                      ation)  e.g. CH.sub.3 CN, DMF, DMSO,                                                   acetone, sulpholane,                                                           with III being conveniently                                                    added slowly to the metal                                                      alkanoate                                                           b 11,                                                                             Conden- Weakly basic medium; especially                                                                20-100° C.                                                                    Fedorynski et al., J. Org.                       sation  by means of alkali carbo-                                                                            Chem. 43 (24), 4682 (1978)                    b 2,                                                                              (oxalkylation)                                                                         nates or alkali bicarbonates                                        b 33       or by means of trialkylamines,                                                 e.g. triethylamine, preferably                                                 in the presence of tetraalkyl-                                                 ammonium salts or crown ethers                                                 as catalysts.                                                                  in polar solvents, e.g.                                                        CH.sub.3 CN, DMF, DMSO, acetone,                                               sulpholane; or in water; or                                                    also in the absence of solvent                                                 III or III' or III": IV                                                        = 1:1-3, esp. 1:1-1.5                                                  Alkylation of                                                                          Alkyl halides/metal carbonates,                                                                20-80° C.                                                                     Organikum, organisch-                            II (basic,                                                                             e.g. alkyl iodides/metal                                                                             praktisches Grundpraktikum,                      non-aqueous)                                                                           carbonates, metal alcoholates                                                                        collective authors, VEB,                                 in aprotic solvents, e.g.                                                                            deutscher Verlag der                                     acetonitrile, DMF, DMSO                                                                              Wissenschaften, Berlin,                                                        1967, pages 469 et seq.                       __________________________________________________________________________      (1) According to methods known per se                                    

The compounds of formula I are for the most part known. They are odorant and/or flavouring substances, whereby in this respect the following compounds stand in the foreground of interest: ##STR8##

The compounds marked with asterisks as novel; these compounds are also an object of the present invention, as are odorant and/or flavouring substance compositions containing the novel compounds and the use of the novel compounds as odorant and/or flavouring substances.

The organoleptic properties of the novel compounds are as follows:

    ______________________________________                                                    Odour.sup.(1)                                                                               Flavour.sup.(2)                                        ______________________________________                                         2-Hydroxy-3,4,5-tri-                                                                        sweet, burnt,  sweet, burnt,                                      methyl-2-cyclopenten-                                                                       powerful,      spicy,                                             1-one        corylone-like, corylone-like,                                                  after caramel, after caramel,                                                  maple          maple, coffee,                                                                 bread,                                                                         liquorice                                          5-Ethyl-2-hydroxy-                                                                          burnt,         very similar to                                    3,4-dimethyl-2-cyclo-                                                                       spicy, powerful,                                                                              that above                                         penten-1-one after caramel,                                                    + tautomeric form                                                                           coffee, nuts                                                      2-Hydroxy-3,4,4-tri-                                                                        weaker by twice than                                              methyl-2-cyclopenten-                                                                       above                                                             1-one                                                                          ______________________________________                                          .sup.(1) 10% in C.sub.2 H.sub.5 OH                                             .sup.(2) 3 ppm in H.sub.2 O                                              

A comparison of the novel trimethyl derivative with the most well known of the above flavouring substances, 2-hydroxy-3-methyl-2-cyclopenten-1-one ("Corylone"), see S. Arctander, Perfume and Flavor Chemicals, Montclair N.J. 1969; indicated that in the first case the flavour intensity is 20 times greater (measured in both instances in water, c=1-10 ppm).

Compared with the known, structurally related odorant substance 2-hydroxy-3,4,4-trimethyl-2-cyclopenten-1-one (Eu-A 80 600), only the novel trimethyl derivative produces surprising effects in compositions of the fougere, rose, tobacco and leather type.

The novel compounds of formula I used in accordance with the invention as odorant and/or flavouring substances enrich the olfactory character of odorant substance compositions, especially of fougere-like, chypre-like, woody, animal compositions or bases. The compounds I combine with numerous known odorant substance ingredients of natural of synthetic origin, whereby the range of the natural raw substances can embrace not only readily volatile but also moderately volatile and difficulty ("slightly") volatile components and that of the synthetics can embrace representatives from practically all classes of substances, as is evident from the following compilation:

Natural products: Basil oil, tree moss absolute, mugwort oil, bergamot oil, cassis bud absolute, castoreum, cedarwood oil, ciste labdanum, civet, coriander oil, oak moss, elemi oil, pine needle oil, galbanum, geranium oil, clove oil, jasmin absolute and its synthetic substitute, jonquille absolute, camomile oil, labdanum, lavender oil, mandarin oil, mastix absolute, mentha citrata oil, myrrh oil, palmarosa oil, patchouli oil, petitgrain oil Paraguay, sandalwood oil, thyme oil, vassoura oil, musk infusion, styrax, birch tar, vetiver oil, frankincense, ylang-ylang oil, lemon oil, civet oil, etc.

Alcohols: Citronellol, Dimetol® (3,6-dimethyl-heptan-2-ol), geraniol, cis-3-hexenol, linalool, Nonadyl® (6,8-dimethyl-nonan-2-ol), phenylethyl alcohol, rhodinol, Sandela® (3-isocamphyl -5-cyclohexanol), Sandalore® (3-methyl-5-(2',2',3'-trimethyl-cyclopent-3'-en-1'-yl)-pentan-2-ol), terpineol, etc.

Aldehydes: α-Amylcinnamaldehyde, cyclamen aldehyde, decanal, dodecanal, heliotropin, α-hexylcinnamaldehyde, hydroxycitronellal, lyral, Adoxal® (2,6,10 -trimethyl-undec-9-en-1-al), undecanal, ω-undecylene aldehyde, vanillin, etc.

Ketones: Isoraldeine® (isomethyl-α-ionone), α-ionone, β-ionone, 3-prenylisocaranone, Vertofix® (=acetylated cedarwood oil), p-methylacetophenone, etc.

Esters: Ethyl acetoacetate, amyl salicylate, benzyl acetate, cedryl acetate, cinnamyl formate, citronellyl acetate, geranyl acetate, cis-3-hexenyl acetate, cis-3-hexenyl benzoate, linalyl acetate, linalyl anthranilate, methyl dihydrojasmonate, Methambrat® (1-acetoxy-1-methyl-2-sec. -butylcyclohexane), Myraldylacetat® (4-(4-methyl-3-pentenyl)-cyclohex-3-en-1-yl-carbinyl acetate), phenoxyethyl isobutyrate, phenylethyl tiglate, styrallyl acetate, terpenyl acetate, 2,3,6,6-tetramethyl-cyclohex-2-ene-carboxylic acid ethyl ester, 3,6,6-trimethyl-2-ethyl-cyclohex-2-ene-carboxylic acid ethyl ester, vetivenyl acetate, ortho-tert.butylcyclohexyl acetate, etc.

Various: Musk ambrette, coumarin, epoxycedrene, eugenol, Fixolide® (1,1,2,4,4,7-hexamethyl-6-acetyl-1,2,3,4-tetrahydronaphthalene), Galaxolid® (1,3,4,6,7,8-hexahydro-4,6,6,7,7,8-hexamethyl-cyclopenta-γ-2-benzopyran), heliotropin, indole, indolene, isoeugenol, isobutylquinoline, jasmonyl (1,3-diacetoxy-nonane), musk ketone, limonene, p-menthane-8-thiol-3-one, Madrox® (1-methylcyclododecyl methyl ether), methyleugenol, Musk 174® (12-oxahexadecanolide), γ-nonalactone, γ-undecalactone, etc.

The compounds of formula I (or their mixtures) can be used in wide limits which can extend in compositions, for example, from 0.1 (detergents) -30% (alcoholic solutions). These values are not intended to represent limiting values, as the experienced perfumer can also achieve effects with even lower concentrations or can synthesize novel complexes with even higher dosages. The preferred concentrations range between 0.1 and 25%. The compositions manufactured with I can be used for all kinds of perfumed consumer goods (eau de cologne, eau de toilette, extracts, lotions, creams, shampoos, soaps, salves, powders, toothpastes, mouth washes, deodorants, detergents, tobacco, etc).

The compounds I (or their mixtures) can accordingly be used for the manufacture of compositions and, as the above compilation shows, using a wide range of known odorant substances or odorant substance mixtures. In the manufacture of such compositions the odorant substances or odorant substance mixtures mentioned above can be used according to methods known to the perfumer, such as e.g. according to W. A. Poucher, Perfumes, Cosmetics, Soaps 2, 7th Edition, Chapman and Hall, London 1974.

The novel compounds of formula I are also excellently suited for use in flavours of the widest variety of kinds, but especially for the flavouring of tobacco.

As flavouring substances the compounds I can be used, for example, for the production or improvement, intensification, enhancement or modification of fruit flavours, e.g. blueberry or blackberry flavours, of walnut, hazelnut, almond, chocolate, coffee and milk flavours, etc. As fields of use for these flavours their come into consideration, for example, foodstuffs (yoghurt, confectionery etc.), semi-luxury consumables ("Genussmittel") (tea, tobacco, etc.) and drinks (lemonade etc.).

The pronounced flavour qualities of the compounds I enable them to be used as flavouring substances in low concentrations. A suitable dosage embraces, for example, the range of 0.01 ppm-100 ppm, preferably the range of 0.01 ppm-20 ppm, in the finished product, i.e. the flavoured foodstuff, semi-luxury consumable or drink.

In the flavouring of, for example, tobacco the dosage can, however, also lie higher and can embrace a wider range, for example the range of 1 to 1000 ppm, preferably 30-100 ppm.

The compounds can be mixed with the ingredients used for flavouring compositions or added to such flavourants in the usual manner. Under the flavourants used in accordance with the invention there are to be understood flavouring substance compositions which can be diluted or dispersed in edible materials in a manner known per se. They contain, for example, about 0.1-10, especially 0.5-3 wt.%. they can be converted according to methods known per se into the usual forms of use such as solutions, pastes or powders. The products can be spray-dried, vacuum-dried or lyophilized.

The known flavouring substances conveniently used in the manufacture of such flavourants are either already contained in the above compilation or can be concluded readily from the literature, such as e.g. J. Merory, Food Flavorings, Composition, Manufacture and Use, Second Edition, The Avi Publishing Company, Inc., Westport, Conn. 1968, or G. Fenaroli, Fenaroli's Handbook of Flavor Ingredients, Second Edition, Volume 2, CRC Press, Inc., Cleveland, Ohio 1975.

For the manufacture of such usual forms of use there come into consideration, for example, the following carrier materials, thickening agents, flavour improvers, spices and auxilliary ingredients, etc:

Gum arabic, tragacanth, salts or brewers' yeast, alginates, carrageen or similar absorbents; indoles, maltol, dienals, spice oleoresins, smoke flavours; cloves, diacetyl, sodium citrate; monosodium glutamate, disodium inosine-5'-monophosphate (IMP), disodium guanosine-5-phosphate (GMP); or special flavouring substances, water, ethanol, propylene glycol, glyercine.

EXAMPLE 1

(a) 113.4 g (2.1 mmol) of sodium methylate are suspended in 150 ml of acetonitrile. 150.5 g (1 mol) of methyl 4-chloroacetoacetate are thereupon allowed to flow in within 5 minutes. The temperature rises, but it is held at 68°-70° C. by cooling. The mixture is subsequently stirred at 70° C. for a further 25 minutes. The reaction mixture is poured into a solution of 350 ml of distilled water and 9 g of acetic acid and held at a pH value of 6-7 by the addition of a total of 83 ml of 32% hydrochloric acid. The organic layer is separated in a separating funnel and the aqueous layer is extracted 3 times with 200 ml of acetonitrile each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. The crude product distils at 55°-57° C./0.6 mbar. There are obtained 132.34 g (90.6 %) of methyl 4-methoxy-acetoacetate.

IR (liq. film): 3450^(m), 1750^(s), 1700^(s), 1660^(m) cm⁻¹

NMR (CDCl₃)60MHz: 3.44 (s/3H), 3.52 (s/2H), 3.76 (s/3H), 4.10 (s/2H) ppm

MS (m/e): 146 (M⁺), 115, 101, 59, 45 (100%).

(b) 165.8 g (1.2 mol) of potassium carbonate and 4.6 g (0.02 mol) of benzyltriethylammonium chloride are suspended in 500 ml of acetonitrile. While stirring there are added thereto 146.1 g (1 mol) of methyl 4-methoxy-acetoacetate and there are added dropwise thereto within 10 minutes 138.8 g (1.5 mol) of chloroacetone. The mixture is stirred at 20°-25° C. for a further 7 hours. The reaction mixture is poured on to 1 liter of 10% NaH₂ PO₄ solution/ice (pH value=5) and extracted 3 times with 500 ml of ethyl acetate each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator to give 206.30 g (100%) of methyl 4-methoxy-2-acetonylacetoacetate, content: 84.3%; b.p. 104°-105° C./0.06 mbar.

IR (liq. film): 3610^(m), 1745², 1715^(s), 1630^(m) cm⁻¹

NMR (CDCl₃)60MHz: 2.20 (s/3H), 3.01-3.21 (m/2H), 3.45 (s/3H), 3.73 (s/3H), 4.00-4.23 (m/1H), 4.28 (s/2H) ppm

MS (m/e): 202 (M⁺,) 157, 125, 97, 55, 45 (100%).

(c) 201.3 g (0.997 mol) of crude methyl 4-methoxy-2-acetonylacetoacetate are held at reflux temperature for 3 hours with 2.12 liters (0.5 mol) of 2.5% Na₂ CO₃ solution. The reaction mixture is extracted 3 times with 100 ml of CH₂ Cl₂ each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator to give 99.90 g (79.5%) of 2-methoxy-3-methyl-2-cyclopenten-1-one, content 84.2%; b.p. 82°-84° C./27 mbar.

IR (liq. film): 1700², 1645^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 2.00 (s/3H), 2.40 (s/4H), 3.88 (s/3H) ppm

MS (m/e): 126 (M⁺, 100%), 111, 97, 83, 55.

(d) 94.8 g (0.75 mol) of crude 2-methoxy-3-methyl-2-cyclopenten-1-one are held at reflux temperature for 5 hours with 1.896 kg (20 fold amount by weight) of 5N hydrochloric acid. The reaction mixture is extracted 3 times with 300 ml of CH₂ Cl₂ each time. The organic phases are extracted twice with 500 ml of 2N sodium hydroxide solution each time. The combined NaOH extracts are adjusted to a pH value of 5 with concentrated hydrochloric acid while cooling and then extracted 3 times with 300 ml of CH₂ Cl₂ each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. After recrystallization from acetone/water 1:1 there are obtained 57.66 g (68.4%) of 2-hydroxy-3-methyl-2-cyclopenten-1-one; m.p. 100°-102° C.

IR (CHCl₃): 3500^(m), 3310^(w) (broad), 1710^(s), 1660^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 2.02 (s/3H), 2.45 (s/4H), 7.00 (s, broad/1H) ppm

MS (m/e): 112 (M⁺, 100%), 97, 84, 69, 55, 41.

EXAMPLE 2

(a) 108 g (1.1 mol) of potassium acetate and 11.4 g (0.05 mol) of benzyltriethylammonium chloride are suspended in 900 ml of acetonitrile, treated with 50 ml of acetic acid and heated to reflux temperature. Within 31/2 hours there are added dropwise thereto 150.5 g (1 mol) of methyl 4-chloroacetoacetate in 100 ml of acetonitrile and the mixture is subsequently held at reflux temperature for 4 hours. The reaction mixture is washed 3 times with 200 ml of 5% NaH₂ PO₄ solution each time and the aqueous phases are back-extracted with 200 ml of CH₂ Cl₂. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. The crude product distils at 76°-85° C./0.6 mbar and gives 106.17 g (61%) of methyl 4-acetoxyacetoacetate.

IR (liq. film): 3610-3450^(w) (complex), 1740^(s) (broad) 1650^(m) (s)

NMR (CDCl₃)60 MHz: 2.19 (s/3H), 3.53 (s/2H), 3.78 (s/3H), 4.80 (s/2H) ppm

MS (m/e): 174 (M⁺), 132, 101, 74, 59, 43 (100%)

(b) 63.6 g (0.6 mol) of sodium carbonate and 2.3 g (0.01 mol) of benzyltriethylammonium chloride are suspended in 250 ml of acetonitrile. While stirring there are added thereto 87.0 g (0.5 mol) of methyl 4-acetoxyacetoacetate and there are added dropwise thereto within 5 minutes 69.4 g (0.75 mol) of chloroacetone. The mixture is stirred at 20°-25° C. for a further 46 hours. The reaction mixture is poured on to 1 liter of 10% NaH₂ PO₄ solution/ice (pH value=5) and extracted 3 times with 300 ml of ethyl acetate each time. The combined organic phases are dried over magnesium sulphate and concentrated completely on a rotary evaporator to give 105.9 g (92%) of methyl 4-acetoxy-2-acetonylacetoacetate, content 76.9%; b.p. 119°-121° C./0.06 mbar.

IR (liq. film): 1730^(s) (broad, complex) cm⁻¹

NMR (CDCl₃)60 MHz: 2.18 (s/3H), 2.21 (s/3H), 3.09-3.22 (m/2H), 3.76 (s/3H), 4.11 (t/1H), 4.97 (s/2H) ppm

MS (m/e): 170, 157, 125, 97, 87, 43 (100%).

(c) 230 mg (1 mol) of crude methyl 4-acetoxy-2-acetonylacetoacetate are held at reflux temperature for 1 hour with 2 ml (0.19 mmol) of 1% Na₂ CO₃ solution, whereby the PH value drops to 6. Solid Na₂ CO₃ is added thereto until the pH value remains at 11-12 and the mixture is held at reflux temperature of a further 1 hour. The reaction mixture is poured on to 10 ml of 10% NaH₂ PO₄ solution/ice (pH value=5) and extracted 3 times with 20 ml of CH₂ Cl₂ each time. The combined organic phases are dried with magnesium sulphate and concentrated on a rotary evaporator to give 60.2 mg (53.7%) of 2-hydroxy-3-methyl-2-cyclopenten-1-one, content: 95.7%; m.p. 100°-102° C.

IR (CHCl₃): 3500^(m), 3310^(w) (broad), 1710^(s) 1660^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 2.02 (s/3H), 2.45 (s/4H) ppm.

EXAMPLE 3

(a) 127.2 g (1.2 mol) of sodium carbonate and 4.6 g (0.02 mol) of benzyltriethylammonium chloride are suspended in 800 ml of acetonitrile. While stirring there is added dropwise thereto within 8 hours a solution of 150.5 g (1 mol) of methyl 4-chloroacetoacetate and 138.8 g (1.5 mol) of chloroacetone in 200 ml of acetonitrile. The mixture is stirred at 20°-25° C. for a further 15 hours. The reaction mixture is poured into 750 ml of 2N HCl (pH value=1) and extracted three times with 300 ml of ether. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. The residue is treated with 200 ml of ether, the precipitated 2,5-bimethoxycarbonyl-1,4-cyclohexanedione is filtered off under suction and the filtrate is again concentrated. The crude product is column chromatographed on silica gel with ether/hexane 1:1 and gives 32.28 g (15.6%) of methyl 4-chloro-2-acetonylacetoacetate.

IR (liq. film): 3630-3400^(w) (complex), 1750^(s), 1715^(s), 1660^(m) cm⁻¹

NMR (CDCl₃)60 MHz: 2.20 (s/3H), 3.10-3.30 (m/2H), 3.78 (s/3H), 4.12-4.33 (m/1H), 4.50 (s/2H) ppm

MS (m/e): 206 (M⁺), 175, 157, 125, 97, 87, 77, 49, 43 (100%).

(b) 6.20 g (30 mmol) of methyl 4-chloro-2-acetonylacetoacetate are held at reflux temperature for 1 hour with 63.6 g (15 mmol) of 2.5% Na₂ CO₃ solution. The reaction mixture is poured into 30 ml of 1N HCl and extracted 3 times with 50 ml of CH₂ Cl₂. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. The crude product is column chromatographed on silica gel with ether/hexane/CH₂ Cl₂ 1:1:3 and gives 0.80 g (20.4%) of 2-chloro-3-methyl-2-cyclopenten-1-one, content 93.2%; m.p. 37°-39° C.

IR (CHCl₃): 1715^(s), 1625^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 2.20 (s/3H), 2.60 (m/4H) ppm

MS (m/e): 130 (M⁺), 115, 102, 95, 67 (100%).

(c) 0.72 g (5.5 mmol) of 2-chloro-3-methyl-2-cyclopenten-1-one is stirred at room temperature for 1 hour with 27.5 ml (27.5 mmol) of 1N sodium hydroxide solution. The reaction mixture is brought to a pH value of 3 with concentrated hydrochloric acid and extracted 3 times with 20 ml of CH₂ Cl₂. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. After recrystallization from ether/hexane 1:1 there is obtained 0.47 g (76.3%) of 2-hydroxy-3-methyl-2-cyclopenten-1-one; m.p. 101°-102° C.

IR (CHCl₃): 3500^(m), 3310^(w) (broad), 1710^(s), 1660^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 2.62 (s/3H), 2.45 (s/4H), 5.80 (s, broad/1H) ppm

MS (m/e): 112 (M⁺, 100%), 97, 84, 69, 55, 41.

EXAMPLE 4

(a) See Example 1(a).

(b) 16.58 g (120 mmol) of potassium carbonate and 0.46 g (2 mmol) of benzyltriethylammonium chloride are suspended in 50 ml of acetonitrile. While stirring there are added thereto 14.60 g (100 mmol) of methyl 4-methoxyacetoacetate and there are added dropwise thereto within 10 minutes 15.97 g (150 mmol) of 3-chloro-2-butanone. The mixture is stirred at 20°-25° C. for a further 65 hours. The reaction mixture is poured on to 70 ml of 4N HCl/ice (pH value=1) and extracted 3 times with 100 ml of ethyl acetate each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. The crude product distils at 95° C./0.05 mbar and gives 6.67 g (42%) of methyl 4-methoxy-2-[1-methylacetonyl]-acetoacetate.

IR (liq. film): 3620-3400^(w) (broad), 1745^(s), 1715^(s), 1635^(w) cm⁻¹

NMR (CDCl₃)60 MHz: 1.08+1.16 (2d/3H), 2.20+2.23 (2s/3H), 3.15-3.55 (m/1H), 3.41+3.44 (2s/3H), 3.85-4.06 (m/1H), 4.18+ 4.21 2s/2H) ppm

MS (m/e): 216 (M⁺), 171, 139, 111, 69, 45 (100%).

(c) 2.16 g (10 mmol) of methyl 4-methoxy-2-[1-methylacetonyl]-acetoacetate are held at reflux temperature for 2 hours with 21.2 ml (5 mmol) of 2.5% Na₂ CO₃ solution. The reaction mixture is extracted 3 times with 25 ml of CH₂ Cl₂ each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator to give 1.40 g (100%) or 2-methoxy-3,4-dimethyl-2-cyclopenten-1-one, content 96%.

IR (liq. film): 1700^(s), 1640^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 1.19 (d/3H), 1.96 (s/3H), 1.72-2.83 (m/3H), 4.91 (s/3H) ppm.

(d) 0.70 g (5 mmol) of crude 2-methoxy-3,4-dimethyl-2-cyclopenten-1-one is held at reflux temperature for 3 hours with 7 g (10 fold amount by weight) of 5N hydrochloric acid. The reaction mixture is extracted 3 times with 50 ml of CH₂ Cl₂ each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator to give 0.45 g (71.4%) of 2-hydroxy-3,4-dimethyl-2-cyclopenten-1-one, content 90.6%. The data for this material are:

IR (CHCl₃): 3500^(m), 3310^(w) (broad), 1710^(s), 1660^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 1.19 (d/3H), 1.99 (s/3H), 1.76-2.83 (m/3H), 6.02 (s, broad/1H) ppm.

The compound can be purified in accordance with Example 1.d).

Unless noted to the contrary, the content determinations were effected by gas chromatography.

Unless noted to the contrary, the IR, NMR and MS data were determined on purified material, for example material purified by crystallization or distillation.

EXAMPLE 5

(a) 1.66 g (12 mmol) of potassium carbonate and 0.04 g (0.2 mmol) of benzyltriethylammonium chloride are suspended in 5 ml of acetonitrile. While stirring there are added thereto 1.60 g (10 mmol) of methyl 4-methoxy-2-methylacetoacetate and there are then added dropwise thereto within 15 minutes 1.39 g (15 mmol) of chloroacetone. The mixture is stirred at 20°-25° C. for a further 21 hours. The reaction mixture is poured into 20 ml of 2N HCl (pH value=1) and extracted 3 times with 20 ml of ethyl acetate each time. The combined organic phases are dried over sodium sulphate and evaporated on a rotary evaporator. The crude product distils at 95° C./0.03 mbar. There results 0.83 g (38.4%) of methyl 4-methoxy-2-acetonyl-2-methylacetoacetate.

IR (liq. film): 1745^(s) (shoulder), 1720^(s), 1630^(w) cm⁻¹

NMR (CDCl₃)60 MHz: 1.45 (s/3H), 2.12 (s/3H), 3.15 (s/2H), 3.40 (s/3H), 3.71 (s/3H), 4.38 (s/2H) ppm

MS (m/e): 216 (M⁺), 184, 171, 143, 111, 45, 43, (100%).

(b) 5.40 g (25 mmol) of methyl 4-methoxy-2-acetonyl-2-methylacetoacetate are held at reflux temperature for 21/2 hours with 106 ml (12.5 mmol) of 2.5% Na₂ CO₃ solution. The reaction mixture is extracted 3 times with 150 ml of CH₂ Cl₂ each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator to give 2.66 g (76%) of 2-methoxy-3,5-dimethyl-2-cyclopenten-1-one, content: 96.7%.

IR (liq. film): 1705^(s), 1650^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 1.18 (d/3H), 1.98 (s/3H), 1.80-3.00 (m/3H), 3.90 (s/3H) ppm.

(c) 2.15 g (15.36 mmol) of crude 2-methoxy-3,5-dimethyl-2-cyclopenten-1-one are held at reflux temperature for 2 hours with 21.50 g (=10 fold amount by weight) of 5N hydrochloric acid. The reaction mixture is extracted 3 times with 50 ml of CH₂ Cl₂ each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. After recrystallization from ether/hexane 1:1 there are obtained 1.05 g (54.2%) 2-hydroxy-3,5-dimethyl-2-cyclopenten-1-one; m.p. 92°-93° C.

IR (CHCl₃): 3500^(m), 3310^(m) (broad), 1710^(s), 1660^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 1.18 (d/3H), 2.00 (s,3H), 1.80-3.00 (m/3H), 6.40 (s,1H) ppm

MS (m/e): 126 (M⁺, 100%), 111, 98, 83, 79, 69, 55, 43.

EXAMPLE 6

(a) 15.2 g (110 mmol) of potassium carbonate and 0.46 g (2 mmol) of benzyltriethylammonium chloride are suspended in 100 ml of acetonitrile. While stirring there are added thereto 20.2 g (100 mmol) of methyl 4-methoxy-2-acetonylacetoacetate and the mixture is heated to 60° C. Within 100 minutes there are added dropwise thereto 18.7 g (120 mmol) of ethyl iodide and the mixture is stirred at 60° C. for a further 24 hours. The suspension is then poured into a solution of 6.9 g (50 mmol) of potassium carbonate in 300 ml of water and then heated at reflux for 3 hours. The cooled reaction mixture is extracted 3 times with 100 ml of ether. The combined organic phases are dried over magnesium sulphate, concentrated on a rotary evaporator and thus give 12.92 g (84%) of 5-ethyl-2-methoxy-3-methyl-2-cyclopenten-1-one, content (GC): 97%. Boiling point 95° C./14 mbar.

IR (liq. film): 1700^(s), 1645^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 0.95 (t/3H), 2.02 (s/3H), 1.4-2.9 (m/5H), 3.9 (s, 3H) ppm.

(b) 12.8 g (83 mmol) of crude 5 -ethyl-2-methoxy-3-methyl-2-cyclopenten-1-one are held at reflux temperature for 2 hours with 128 g of 5N hydrochloric acid. The cooled reaction mixture is extracted 3 times with 100 ml of CH₂ Cl₂. The combined phases are dried over magnesium sulphate and concentrated on a rotary evaporator. The crude product is distilled at 47°-48° C./0.03 mbar and yields 9.09 g (78.2%) of a mixture of 5-ethyl-2-hydroxy-3-methyl-2-cyclopenten-1-one (isomer A) and 3-ethyl-2-hydroxy-5-methyl-2-cyclopenten-1-one (isomer B) in the ratio of about 7:3, content (GC): isomer A 70.2%, isomer B 28.8%.

IR (CHCl₃): 3500^(m), 330^(m) (broad), 1705^(s), 1655^(s) cm⁻¹

NMR (CDCl₃)400 MHz: Isomer A: 0.95 (t/3H), 1.43 (m/1H), 1.82 (m/1H), 2.02 (s/3H), 2.12 (m/1H), 2.35 (m/1H), 2.60 (m/1H), 6.5 (s, broad/1H) ppm. Isomer B: 1.15 (t/3H), 1.18 (d/2H), 2.03 (m/1H), 2.43 (m/1H), 2.45 (q/2H), 2.71 (m/1H), 6.5 (s, broad/1H) ppm.

MS (m/e): 140 (M³⁰), 125, 112, 107, 97, 94 (100%).

EXAMPLE 7

(a) 15.20 g (110 mmol) of potassium carbonate and 0.46 g (2 mmol) of benzyltriethylammonium chloride are suspended in 100 ml of acetonitrile. While stirring there are added thereto 21.60 g (100 mmol) of methyl 4-methoxy-2-[1 -methylacetonyl]-acetoacetate, the mixture is heated to 60° C. and 28.39 g (200 mmol) of methyl iodide are added dropwise thereto within 30 minutes. The mixture is stirred at 60° C. for a further 16 hours; then 6.91 g (50 mmol) of potassium carbonate and 7.10 g (50 mmol) of methyl iodide are again added and the mixture is stirred at 60° C. for a further 21 hours. 6.90 g (50 mmol) of potassium carbonate in 300 ml of distilled water are now added thereto. The reaction mixture is held at reflux temperature for 6 hours. It is then extracted 3 times with 100 ml of ether each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. The crude product distils at 70°-78° C./12 mm and yields 6.03 g (39.2%) of 2-methoxy-3,4,5-trimethyl-2-cyclopenten-1-one.

IR (liq. film): 1700^(s), 1640^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 1.15 (d/6H), 1.92 (s/3H), 1.60-2.80 (m/2H), 3.88 (s/3H) ppm,

MS (m/e): 154 (M⁺), 139 (100%), 126, 111, 96, 79, 67, 55, 41.

(b) 5.39 g (35 mmol) of 2-methoxy-3,4,5-trimethyl-2-cyclopenten-1-one are held at reflux temperature for 90 minutes with 53.9 g (10 fold amount by weight) of 5N hydrochloric acid. The reaction mixture is extracted 3 times with 50 ml of ether each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. The crude product is distilled at 45°-48° C./0.03 mbar and yields 3.57 g (72.9%) of 2-hydroxy-3,4,5-trimethyl-2-cyclopenten-1-one.

IR (CHCl₃): 3500^(m), 3310^(w) (broad), 1710^(s), 1660^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 1.15 (d/6H), 1.96 (s/3H), 1.60-2.80 (m/2H), 7.10 (s, broad/1H) ppm

MS (m/e): 140 (M⁺), 125 (100%) 112, 97, 83, 79, 69, 55, 43.

EXAMPLE 8

(a) 67.99 g (492 mmol) of potassium carbonate and 1.87 g (8.2 mmol) of benzyltriethylammonium chloride are suspended in 500 ml of acetonitrile. 59.86 g (410 mmol) of methyl 4-methoxyacetoacetate are added thereto while stirring. 65.50 g (615 mmol) of 1-chloro-2-butanone are added dropwise thereto within 30 minutes and the mixture is stirred at 20°-25° C. for 23 hours. The reaction mixture is poured into 1 l of 1N HCl (pH value=1) and extracted 3 times with 700 ml of ethyl acetate each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. The crude product distils at 115° C./0.05 mbar. There results 49.01 g (55.3%) of methyl 4-methoxy-2-(2-oxobutyl)-acetoacetate.

IR (liq. film): 1740^(s), 1720^(s), 1630^(m) cm⁻¹

NMR (CDCl₃)60 MHz: 1.08 t/3H), 2.51 (q/2H), 3.12 (m/2H), 3.48 (s/3H), 3.78 (s/3H), 4.15 (m/1H), 4.30 (s/2H) ppm

MS (m/e): 216 (M⁺), 184, 171, 139, 57, 45 (100%).

(b) 21.60 g(100 mmol) of methyl 4-methoxy-2-(2-oxobutyl)-acetoacetate are held at reflux temperature for 8 hours with 212.0 g (50 mmol) of 2.5% Na₂ CO₃ solution. After cooling the reaction mixture is extracted 3 times with 200 ml of CH₂ Cl₂ each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. The crude product is column chromatographed over SiO₂ and gives 4.08 g (29.1%) of 3-ethyl-2-methoxy-2-cyclopenten-1-one.

IR (liq. film): 1700^(s), 1635^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 1.13 (t/3H), 2.43 (s/4H), 2.46 (q/2H), 3.93 (s/3H) ppm

MS (m/e): 140 (M⁺, 100%), 125, 111, 97, 69.

(c) 3.08 g (22 mmol) of 3-ethyl-2-methoxy-2-cyclopenten-1-one are held at reflux temperature for 5 hours with 30.80 g of 5N hydrochloric acid. After cooling the reaction mixture is extracted 3 times with 50 ml of CH₂ Cl₂ each time. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. The crude product is bulb-tube distilled at 0.1 mbar/110° C. and gives 1.82 g (65.7%) of 3-ethyl-2-hydroxy-2-cyclopenten-1-one (melting point 39°-41° C.).

IR (CHCl₃): 3500^(m), 3310^(m) (broad), 1710^(s), 1660^(s) cm⁻¹

NMR (CDCl₃)60 MHz: 1.13 (t/3H), 2.43 (s/4H), 2.46 (q/2H), 6.60 (s, broad/1H) ppm,

MS (m/e): 126 (M⁺, 100%), 111, 77, 83, 69, 55, 43.

EXAMPLE 9

(a) 22.80 g (165 mmol) of potassium carbonate and 0.69 g (3 mmol) of benzyltriethylammonium chloride are suspended in 150 ml of acetonitrile. While stirring 32.42 g (150 mmol) of methyl 4-methoxy-2-(1-methylacetonyl)-acetoacetate are added thereto and the mixture is heated to 60° C. 28.08 g (180 mmol) of ethyl iodide are added thereto within 100 minutes and the mixture is stirred at 60° C. for a further 90 hours. The suspension is then poured into a solution of 10.35 g (75 mmol) of potassium carbonate in 450 ml of water and heated at reflux temperature for 30 hours. The cooled reaction solution is extracted 3 times with 300 ml of CH₂ Cl₂. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. The crude product is distilled at 20 mbar/97°-99° C. and gives 3.61 g (14.3%) of 5-ethyl-2-methoxy-3,4-dimethyl-2-cyclopenten-1-one.

IR (liq. film): 1700^(s), 1640² cm⁻¹

NMR (CDCl₃)60 MHz: 0.82-1.10 (m/3H), 2.20 (d/3H), 1.94 (s/3H), 1.32-2.61 (m/4H), 3.93 (s/3H) ppm

MS (m/e): 168 (M⁺), 153, 140, 125, 108 (100%), 93, 55.

(b) 2.06 g (12.2 mmol) of 5-ethyl-2-methoxy-3,4-dimethyl-2-cyclopenten-1-one are held at reflux temperature for 2 hours with 20.6 g of 5N hydrochloric acid. The cooled reaction solution is extracted 3 times with 50 ml of CH₂ Cl₂. The combined organic phases are dried over magnesium sulphate and concentrated on a rotary evaporator. The crude product is bulb-tube distilled at 1 mbar/104° C. and gives 1.43 g (76.1%) of a mixture of 5-ethyl-2-hydroxy-3,4-dimethyl-2-cyclopenten-1-one (isomer A) and 3-ethyl-2-hydroxy-4,5-dimethyl-2-cyclopenten-1-one (isomer B) in the ratio of about 4:1. Content (GC): isomer A 68.9%, isomer B 17.1%.

IR (liq. film): 3500^(m), 3300^(m) (broad), 1705^(s), 1655^(s) cm⁻¹

NMR (CDCl₃): 0.82-1.10 (m/about 3H), 2.20 (d/about 4H), 1.99 (s/about 3H), 1.32-2.92 (m/about 3H), 6.61 (s, broad/1H) ppm

MS (m/e): 154 (M⁺), 139, 126, 108, 55, 43 (100%).

In the following Examples "compound I" stands for the novel 2-hydroxy-3,4,5-trimethyl-2-cyclopenten-1-one.

EXAMPLE 10

An almond-hazelnut flavour can be made up as follows:

    ______________________________________                                                          Parts by weight                                               ______________________________________                                         Vanillin           25.0    25.0                                                Acetylpyrazine     2.5     2.5                                                 Diacetyl           3.0     3.0                                                 Dimethylresorcinol 3.0     3.0                                                 Furfural           4.0     4.0                                                 Benzaldehyde       8.0     8.0                                                 gamma-Nonalactone  1.0     1.0                                                 Trimethylpyrazine  1.0     1.0                                                 Propylene glycol   922.5   946.5                                               Corylone           30.0    --                                                  Compound I         --      6.0                                                                    1000.0  1000.0                                              ______________________________________                                    

Dosage in a milk drink: 50 gr/100 liter (an analogous dosage applies for a maple, chocolate and coffee flavour, etc.).

In flavours the novel compound I produces sensorically the same effect as about a 5-fold amount of "Corylone". (As mentioned above, the novel compound, quite apart from the flavour intensity examined here, is even 20 times stronger).

EXAMPLE 11 (a)

    ______________________________________                                         Tobacco base                                                                                           Parts by                                                                       weight                                                 ______________________________________                                         o-tert.Butylcyclohexyl acetate                                                                           400                                                  Jasmin oil synth.         300                                                  Musk ketone               40                                                   Sandela Givaudan          40                                                   Styrallyl acetate         30                                                   Coumarin                  20                                                   Isobutylquinoline 10% DPG (dipropylene glycol)                                                           10                                                   Lavender oil              10                                                   Vetiver oil               10                                                   Galbanum oil              10                                                   Vassura oil               10                                                   DPG                       40                                                                             920                                                  ______________________________________                                    

If 10 parts of a 10% solution in ethanol of the compound I is added to the above base, then the composition receives a pleasant warmth; its sweet jasmin note is supplemented by a fresh-herby note.

(b)

    ______________________________________                                         Leather base                                                                                       Parts by weight                                            ______________________________________                                         Sytrax nat. RIFM      250                                                      Castoreum anhydrous   150                                                      Bergamot oil          100                                                      Musk inf. 3% in ethanol                                                                              100                                                      Vetiver oil           100                                                      Labdanum resinoid     100                                                      Birch tar oil dephenolized 10% DPG                                                                   50                                                       Musk ketone           25                                                       Sandalwood oil        10                                                       Vanillin              5                                                        Ciste labdanum        5                                                        DPG                   60                                                                             960                                                      ______________________________________                                    

If a 10% solution of the compound I is added to the above base, then the leather base surprisingly gains a strong smoky note which combines very well with the leather character of the base and supplements this harmonically without the birch tar oil appearing in an unpleasant manner.

(c)

    ______________________________________                                         Fougere base                                                                                     Parts by weight                                              ______________________________________                                         Lavender oil        200                                                        Linalyl acetate     150                                                        Tree moss absolute  60                                                         Coumarin            50                                                         Patchouli oil       30                                                         Rhodinol extra ex geranium oil                                                                     30                                                         Methyl dihydrojasmoate                                                                             30                                                         Musk ketone         30                                                         Vetivenyl acetate   30                                                         Geranium BB synth.  30                                                         Amyl salicylate     20                                                         Sandela Givaudan    20                                                         Linalool            20                                                         Benzyl acetate      15                                                         Ylang-ylang oil     15                                                         Eugenol             15                                                         Thyme oil           5                                                          DPG                 50                                                                             800                                                        ______________________________________                                    

If 10 parts of a 10% solution of the compound I are added to the above base, then the herby note of the fougere base is underlined in a pleasant manner and the lavender note is rounded-off finely.

(d)

    ______________________________________                                         Rose base                                                                                       Parts by weight                                               ______________________________________                                         Phenylethyl alcohol                                                                               300                                                         Geraniol           250                                                         Jasmin "lavage"    200                                                         Citronellol extra  100                                                         alpha-Ionone       40                                                          C-10-Aldehyde 10% DPG                                                                             5                                                           C-11-Aldehyde 10% DPG                                                                             5                                                                              900                                                         ______________________________________                                    

If 10 parts of a 10% solution of the compound I are added to this base, then the composition takes on a novel, interesting direction; it now becomes very much more sharp, but without losing in naturalness.

In the above Example the compound I was, moreover, in each instance replaced by the same amount of the known 2-hydroxy-3,4,4-trimethyl-2-cyclopenten-1-one. In all of these cases a negative effect was achieved. In all cases an unpleasant lovage note of the known trimethyl derivative pervaded, which conferred to the composition an undesired "food note". 

I claim: 1.A compound of the formula ##STR9## wherein: R represents C₁₋₄ -alkoxy, chlorine, bromine or C₁₋₄ -alkanoyloxy, R¹ signifies C₁₋₅ -alkyl, the radicals R² each independently represent hydrogen or C₁₋₅ -alkyl, and R³ signifies C₁₋₄ -alkyl.
 2. A compound according to claim 1 wherein:(a) R¹ is selected from the group consisting of methyl, ethyl, propyl and isopropyl, and, (b) R² is selected from the group consisting of hydrogen, methyl, ethyl, propyl and isopropyl.
 3. A compound according to claim 2 which is Methyl 4-methoxy-2-acetonylacetoacetate.
 4. A compound according to claim 2 which is Methyl 4-acetoxy-2-acetonylacetoacetate.
 5. A compound according to claim 2 which is Methyl 4-chloro-2-acetonylacetoacetate.
 6. A compound according to claim 2 which is Methyl 4-methoxy-2-(1-methylacetonyl)-acetoacetate.
 7. A compound according to claim 2 which is Methyl 4-methoxy-2-acetonyl-2-methyl-acetoacetate.
 8. A compound according to claim 2 which is Methyl 4-methoxy-2-(2-oxobutyl)-acetoacetate. 